The vortical wake shed from a flying aircraft can pose hazards for any aircraft that happens to fly into the wake. The turbulence and vortical air velocities of a wake can cause sudden alterations in the aerodynamic forces exerted on an aircraft flying into the wake, resulting in effects that can include buffeting or bumping of the aircraft, sudden changes in attitude of the aircraft, and sudden changes in altitude of the aircraft. The consequences of flying into a wake tend to be of greater concern at low altitudes, such as during takeoff and landing operations at an airport, because there may not be sufficient time and altitude to recover from a sudden wake-induced aircraft motion before the aircraft impacts the ground. Furthermore, the strengths of wakes produced by aircraft tend to be greater during relatively low-speed takeoff and landing operations than during higher-speed flight because the strength of a vortex shed from the tip of a lifting surface is inversely proportional to the air velocity over the surface. Thus, interference from aircraft wake turbulence is a significant problem that can compromise safe operation of an aircraft.
A number of systems have been proposed for detecting, warning of, and/or avoiding contact between an aircraft and the wake of another aircraft. For example, U.S. Pat. No. 5,845,874 describes a system and method for creating visual images of aircraft wake vortices by mathematical modeling of the vortices based on characteristics of the aircraft that is creating them. The vortex modeling also takes into account the effects of atmospheric conditions such as wind on the vortices. One embodiment described in the patent provides a visual "heads-up" display in an aircraft on which the simulated wake vortices are displayed for each aircraft in the vicinity of the subject aircraft. It is said that the display of the wake vortices enables the pilot to "see" the vortices so that he or she can identify and avoid them. A disadvantage of this system is that when many aircraft are sharing the same airspace with the subject aircraft, such as around a busy airport, the heads-up display could become so cluttered with the simulated wakes of the other aircraft that the pilot may have difficulty distinguishing the wakes that could pose a hazard from those that can be safely ignored.